The cellular wireless applications have become more and more diverse and bandwidth-demanding. Thus, there is a constant need for increasing the bandwidth for users. In addition to high bandwidth-demand some applications have also very high requirement for quality of service (QoS). One example of this is video call, wherein the transferred data amount is high and there is a need to keep the video fluent in order to provide pleasant user experience.
Because of this commercial operators have invested to their networks for increasing the capacity. However, the licensed spectrum, supervised by the operators, is a scarce resource of which amount along with the current policy of using the licensed spectrum may not be enough to support huge number of cellular devices and higher QoS requirement traffic in the future. Thus, there is a constant need for finding improvements to the bandwidth and QoS.
One solution to the above mentioned problem is to use unused parts of radio spectrum. One example of unused part of radio spectrum is the white spaces between TV channels.
The TV white space (TVWS) bands are the unused parts of radio spectrum—the TV channels—in the 54-698 MHz range. In the US, for example, the Federal Communications Commission (FCC) has approved the regulated use of the white spaces between and among the unused analog TV channels for unlicensed devices. The potential use of TVWS has been investigated widely in the recent years due to their available large bandwidths at suitable frequencies for different radio applications. In the US, the FCC has regulated licensed or license-exempt TV bands for the secondary-system applications, such as cellular, WiFi and WiMax, on TV Band Devices (TVBD). The highly favorable propagation characteristics of the TV broadcast spectrum, as compared to the 2.4 or 5 GHz bands, allow for wireless broadband deployment with greater range of operation with the ability to pass through buildings, weather, and foliage at lower power levels. Thus, the TV white spaces could be used to provide ubiquitous coverage for municipal wireless networks.
There are multiple available TV channels in the broadcast television frequency bands at 54-60 MHz (TV channel 2), 76-88 MHz (TV channels 5 and 6), 174-216 MHz (TV channels 7-13), 470-608 MHz (TV channels 14-36) and 614-698 MHz (TV channels 38-51), which can be used for TVBD. FCC has defined following requirements for different TV band device types.
1. Fixed Device.
                Operating from fixed location registered to WS database.        Geo-location/database access required.        Max 1 W transmission power (4 W radiated power (EIRP)).        Operating on unoccupied channels between 2 and 51.        Can't operate on the first adjacent channels to TV stations.2. Personal/Portable Devices—Modes II/Mode I.        Can't operate below channel 21.        Do not need to register to WS database.        Operating on unoccupied channels between 21 and 51.        Max 100 mW radiated power (EIRP). (40 mW close to TV station's service area).        Mode II: Geo-location/database access required.        Mode I: Geo-location/database access not required.        A mode II device can accesses to a TV bands database either through a direct connection to the Internet or through an indirect connection to the Internet by way of fixed TVBD or another Mode II TVBD, to obtain a list of available channels.        A mode II device may select a channel itself and initiate and operate as part of a network of TVBDs, transmitting to and receiving from one or more fixed TVBDs or personal/portable TVBDs.        A Mode II device must check its location at least once every 60 seconds while in operation3. Sensing Only Device.        Use spectrum sensing to determine a list of available channels.        Max 50 mW radiated power (EIRP). (40 mW close to TV station's service area).        Operating on unoccupied channels between 21 and 51.        
Timing advance is needed in various mobile communication networks for controlling uplink transmissions from a user equipment (UE) to a base station. In the following Long Term Evolution (LTE) networks are used as an example in describing prior art and the problem, however, the same problem may be present also in different network technologies. In LTE networks timing advance is needed so that uplink transmissions from different users arrive at the eNodeB essentially within the cyclic prefix. eNodeB is a radio base station in control of all radio related functions in the fixed part of the LTE system. Such uplink synchronization is needed to avoid interference between the users with uplink transmissions scheduled on the same sub-frame. The timing advance value is measured from Random Access Channel (RACH) transmission when UE does not have a valid timing advance, that is, the uplink for the UE is not synchronized. Timing advance is also needed when LTE user equipments transmit to eNodeB on TVWS due to the large coverage.
In conventional LTE system timing advance is obtained by doing RACH due initial access, RRC connection re-establishment, handover, downlink data arrival or uplink data arrival.
One problem of doing RACH to get riming advance is that one contention-based RACH may collide with another one, which decreases the spectrum efficiency. Furthermore, there are channels which can only be used by portable devices and sensing devices such as channels which are the first adjacent channels to TV stations. In these channels, only user equipment transmissions to eNodeB and to other user equipments are allowed. In other words these are downlink disabled channels. So doing RACH on these downlink disabled channels is impossible.
Thus, there is a need to find a solution to get timing advance on TVWS due to its specific characteristics and regulatory requirements such as on down-link disabled channels.